<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{
            margin: 0;padding: 0
        }
        html{
            font-size: 31.25vw;
        }
        html,body{
            height: 100%;
        }
        body{
            display: flex;
            flex-direction: column;
        }
        header{
            width: 100%;
            height:  0.44rem;
            background: red;
        }
        nav{
            width: 100%;
            height: 0.35rem;
            background: orange;
        }
        main{
            background: pink;
            flex: 1
        }
        footer{
            width: 100%;
            height: 0.44rem;
            background: green
        }
    </style>
</head>
<body>
    <header></header>
    <nav></nav>
    <main></main>
    <footer></footer>
</body>
</html>